Unable to setup custom javascript detail page button

Question

I am working on detail javascript button in the lead object. But now I am facing the below issue.

Javascript code:

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/24.0/apex.js")}
var parent = "{!Lead.Parent_LeadId__c}";
If(parent === "")
{
alert("pop up"); 
}
else
{
sforce.apex.execute("SwapRecords","ChangeMaster",{ID:"{!Lead.Id}",ID:"{!Lead.Parent_LeadId__c}"});
}

Apex class:

global class SwapRecords {
    webservice static void ChangeMaster(Id changetomaster,Id CurrentMaster)
    {
        List<Lead> UpdateLeads = new List<Lead>();
        for(Lead ls:[Select id,Parent_Lead__c from lead where Parent_Lead__c=:CurrentMaster OR id=:CurrentMaster ])
        {
            If(ls.Id == changetomaster)
            {
                ls.Parent_Lead__c='';
                UpdateLeads.add(ls);
            }
            else
            {
                ls.Parent_Lead__c=changetomaster;
                UpdateLeads.add(ls);
            }
        }
        If(UpdateLeads !=null && !UpdateLeads.isEmpty() )
        {
            update UpdateLeads;
        }
    }
}

Please help where I did wrong

Answer 1

JavaScript is cAsE sEnSiTiVe. In this case, you used If instead of if, and so caused a parsing error later on at the else keyword. You also are not passing the parameters correctly; you need to use the variable name in the Apex method, not its "type".

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/24.0/apex.js")}
var parent = "{!Lead.Parent_LeadId__c}";
if(parent === "") {
  alert("pop up"); 
} else {
  sforce.apex.execute(
    "SwapRecords",
    "ChangeMaster",
    { changetomaster:"{!Lead.Id}",
      CurrentMaster:"{!Lead.Parent_LeadId__c}"
    }
  );
}